Electric control system for dynamoelectric machines with reversible current



Nov.

A. C. HALTER ELECTRIC CONTROL SYSTEM FOR DYNAMOELECTRIC MACHINES WITH REVERSIBLE CURRENT Filed June 1, 1951 Patented Nov. 10, 1953 -UNITED STATES OFFICE ELECTRIC CONTROL sY-s'T'EM FOR DYNA- MOELECTRIC MACHINES *WITH REVERS- IBLE CURRENT Allan G. Halter, 'Milwaukeef wis assignor'to Allis-Chalmers Manufacturing Company, Milwaukee, Wis.

Application June 1, 1951',Serial"N0.-229;299

(Cll 318-142) 4 Claims.

This invention relates in general to improvements-in electric control systems and in particular to means for-controlling a dynamoelectric "machineto limitthe magnitude of an operating "condition thereof.

It is an object of the present invention to provide'an improved control system for a dynamoelectric machine provided with regulating means for maintaining one-operating condition of the machineconstant in which system the operation of the regulating means is abruptly overcome in response to another operatingcondition of the machine attaining a critical limiting value.

- Itis a further object of the present invention to-provide an improvedcontrol system for a dyvnamoelectric machine provided with regulating -means' for maintaining one operating condition of the machine constant, in which system the protective means is operative independently of the regulating means.

Objects and advantages other than those set forth above will be readily apparent from the following description when read in connection with the accompanying drawing, the single figure of-which diagrammatically illustrates the cirsuits and apparatus of theinvention.

-Referring more particularly to the drawing by vcharacter of reference, numeral 3 designates a .dynamoelectric' machine of which an operating condition is to be regulated. Machine 6 is provided withanarmatureta and a field winding 6b energized fromany suitable source such as a battery- 'l th-roughan'adjustable resistor 8. "chinefimay be a motor-of any-suitable type, such as a direct current motor driving any suitable load -?device-such as the rolls 9 of one section of a papermill. Machinefi'is energized from the armature Ha of a generator ll having afield winding 1 lb. Field-winding I ib is energized from the armature [2d of an exciter generator l2 having aself energizing field winding 12b and a pair of "differentially acting field windings I20, 12d. Field winding I2?) is connected across armature In in series with an adjustable resistor 13.

' Field windings I20, 12d are energized from suitable control means such as first electric valve 3 means comprising a pair of triodes l4 and second electric valve means comprising'a similar pair of triodes +5. 'Triodes 14 are each provided with an anodela, acathode'itb, and a control grid p Mc. Each triode i issimilarly provided with an anode i5a, awcatho'de 15b and a control grid 15c.

Anodes "M a are connected parallel witheach :o'ther to one terminal of field winding 12c; and anodes 45w are *similarly connected in parallel with a current limiting resistor H and grids I50 are provided with similar resistors l 8. Grids I areconnected to an output terminal 22- of a cathode follower bridge-circuit 23, and grids [5c are similarly connected to an output terminal 24 of bridge 23. Bridge 23 comprises a pair of fixed resistors 27,28 and a pair of variable resistance elements in the form of electric valve means such as triodes 3|, 32. Triode 3| has an anode am, a cathode 3 lb and a control grid 3lc, and triode 32 has an anode 320 a cathode 32b and a control grid 320. If desired, triodes 3|,s-2 may be mounted within a'common envelope as shown in the drawing. Anodes 3I-a; 32a are connected to the positive terminal of a plate voltage battery 33, and cathodes till), 321) are connected through resistorsfi'i, 28 respectively, to the negative terminal of battery'33. A pair of resistors 29, 30

are serially connected between terminals -22, 24

and aneutral terminal 34 is provided interme- "diate'resistors 29, .30. This intermediate terminal is connected tocathodes Mb, 1512 through a biasing batteryflil and a voltage divider 2| to cause the conductivity of triodes l4, I5 to vary in response to variations in the voltage between terminals 22 '24.

' The potential difference between terminals 22,

24 maybe varied in response to variations in the operating condition being controlled. If it is desired to control the's'peed of machine 6, a

' tachometer generator 35 may be connected to "machine 6 to produce a voltage proportional to the speed oithe machine.

The voltage "of tachometer generator '35 is impressed across a speed'setting voltage div'iderfill and an adjustable portion thereof is compared with the voltage of a suitable reference, such as the voltage impressed across a voltage divider 36 by a battery 31, and the resulting voltage difierence is impressed between the cathode .4lb and the grid Me of a triode il having an anode Ma. Anode Ma is connected throughresistors 43, 34 to the positive terminal of battery 33, and grid 3Ic of triode 3| is oonnectedto a common terminal between resistors :43, 44. A triode l2 similar-to triode 4| may be mounted in a common envelope with tri- 3 ode 4| and the anode 42a thereof connected to battery 33 through a resistor 46. Grid 320 is connected to a terminal 48 between resistor 46 and anode 42a. Suitable biasing means, such as a battery 41, may be connected between cathode 42b and grid 420 to maintain triode 42 in a predetermined state of conductivity.

To prevent an operating condition of machine 6 other than the condition being regulated from substantially exceeding a limiting value, limiting means including a. pair of saturable reactors 56, 51 are associated with the regulating system. Reactor 56 comprises a pair of saturable cores Star, a reactance winding 56b divided into two portions severally wound on the two cores, a control winding 56c likewise divided into two portions and a bias winding 56d similarly comprising two portions. Reactor 51 similarly comprises a pair of saturable cores 57a, a reactance winding 51b, 2. control winding 51c and a bias winding 51d. Reactance windings 56b, 51b are energized in parallel with each other from a suitable source of alternating current, such as the secondary winding Blb of a transformer 6| having a primary winding 6la connected to an alternating current generator 62. Connected in circuit with reactance winding 56b and secondary winding 61b through rectifiers 63 in a resistor 64 which has impressed thereacross a unidirectional signal voltage having a magnitude dependent upon the saturation of reactor 56. A second resistor 65 is similarly connected with reactance winding 51b and winding 61b through rectifiers 66 to produce across resistor 65 a unidirectional signal voltage having a magnitude dependent upon the saturation of reactor 51.

Resistor 64 is connected in the grid circuit of electric valve means comprising a triode H having an anode Ha, a cathode 'IIb and a control grid 'Hc. Resistor 65 is similarly connected in the grid circuit of a triode 12 having an anode 12a, a cathode 12b, and a control grid (20. Resistor 64 is connected between cathode 'IIb and grid He in series with a biasing battery 13 and a resistor 14, while resistor 65 is connected between cathode 12b and grid 120 in series with battery 13 and a resistor 15. Anode Ila is connected to terminal 48, and anode 72a is connected to anode 41a. Cathodes Mb, 121) are connected together to the negative terminal of battery 33 through a conductor 11.

Bias windings 56d, 5111 are serially connected with each other across a suitable source of substantially constant bias voltage, such as a battery 8|. Control windings 55c, 510 are serially connected with each other and a pair of half wave rectifiers 82, 83 across battery 8|. Rectifiers 82, 83 are poled so as to prevent the flow of current from battery 8| through windings 56c, 510. A pair of resistors 86, 8'! are serially connected with each other across battery 81 and a voltage which is a measure of the condition to be limited is impressed between the common terminal of rectifiers 82, 83 and the common terminal of resistors 86, 81. If it is desired to prevent the current in machine 6 from substantially exceeding a predetermined maximum value, an interpole winding 60 of machine 6 may be connected as shown to impress between the common terminals of rectifiers 82, 83, and resistors 86, 81 a voltage which is a measure of the current in machine 6.

In operation, with machines I l and 12 running, machine 6 operates at a speed dependent upon the voltage of armature Ila resulting from the excitation of field winding llb, which excitation is in turn determined by the voltage of armature l2a. Assuming that machine 5 is operating at the desired speed, the voltage impressed by tachometer generator 35 on divider 40 is less than the voltage of voltage divider 36 by a predetermined amount, and this voltage difference is impressed between grid Me and cathode 41b to maintain triode 4| in a predetermined state of conductivity. This predetermined conductivity is selected with respect to the conductivity of triode 42, as determined by bias battery 41, so that terminals 45, 4B are at the same potential when the speed of machine 6 has the desired value.

With terminals 45, 48 at the same potential, grids Bic, 320 are also at equal potentials, resulting in equal conductivities of triodes 3!, 32. Assuming that resistors 2 28 have equal values of resistance, terminals 22, 24 are thus at the same potential and no voltage is impressed upon grids I40, I50 by bridge 23. The conductivities of triodes l4, l5 are therefore determined by the bias voltage across voltage divider 2i, and assuming that resistor I3 is adjusted so that self exciting field Winding lZb supplies all of the excitation required to maintain the voltage of armature 12a at any given value, divider 2! may be adjusted so that triodes l4, l5 are rendered partially conductive to a preselected extent. Under these conditions, equal currents are supplied to diiferentially acting field windings 12c, 12d and field winding 12b maintains the voltage of armature 12a at the value required to maintain the speed of machine 6 at the desired value.

During the above described operation of the system, interpole winding 60 impresses between the common terminal of rectifiers 82, 83 and the common terminal of resistors 86, 8'! a voltage proportional to the current in machine 6. This voltage, when generator H is supplying current to machine 6, acts cumulatively on winding 560 with respect to the voltage of resistor t5 and acts differentially with respect to the voltage of resistor 81 on winding Elc. Rectifier 82- prevents the flow of current through winding 560 under these conditions and rectifier 83 permits current to flow through winding 510 only when the voltage across winding 60 extends the voltage of resistor 81. Therefore, during the above described operation, if the current in machine 6 remains below the maximum value, the voltage of winding 60 is less than the voltage of resistor 81 and no current flows through windings 56c, 51c.

fhe bias current supplied by battery 8| to bias windings 55d, 57d produces in windings 56d, 57d magnetomotive forces which cancel the magnetomotive forces of reactance windings 56b, 57b, respectively, when no current is flowing in control windings 56c, 510, so that substantially no current flows through reactance windings 56b, 571) under these conditions. With substantially no current flowing through windings 56b, 51b, the voltage drops across resistors 64, 55 are negligible, so that battery .53 maintains triodes ll, 12 nonconductive and without effect on the regulating system.

If the speed of machine 6 increases above the desired value, the voltage impressed across divider 40 by tachometer generator 35 increases to render grid Me less negative and thereby increase the conductivity of triode 4!. An increase in conductivity of triode 4| decreases the potential of terminal 45 and the potential of grid 3Ic to sesame decrease-- the pdtentiarbf terminal Ti -with re- "spectto-"thepotential of terminald 4. Grids -l 5c moving the adjustable tap divider 40.

' A sequence-oroperations-converse to that de- "scribed aboveoccurs whenthe speed-of-machine '6 decreases below the desired vaIue-oc'Whenthe "speed setting is raised by moving -the adjustable tap'of divider ll).

' -If, during accelerationofmachine 6; the ma- =chine armature current tends to exceed the limiting-value; the voltage across interpole winding 60 increases above the voltage of resistor Bland "rectifier 83 thereupon permits current to iiow through control winding 510.

This current in COIltIO1-WiIldlI-lg 5l-c produces a magnetomotive -fo'rce which opposes the magnetomotive force of winding 51d and aids the magnetomotive force of-winding 51b to lower thereactance of reactance --winding- 51b to permita substantial current to flow through winding 51b and resistor '65. The

saturating actionof' control winding 1 510 is strengthened by" the self-saturating action of r'ectifie'rs 66, so that as'mall currentin control "winding" 510 causes asubstantial current to flow -in' reactance winding 51b and resistor 65. i This current in resistor 65 produces a voltage thereacross which renders triode 12 abruptly conductive so that the potential ofanode- 4ia, to which anode 12a" is connected, and the potential of terminal 45, are abruptly lowered. A decrease in the potential of terminal 45 lowers the potential of'grid 3-lcto unbalance bridge 23 and render terminal 24 positive'with respect to terminal 22. Triodes l5 are thereupon rendered more cond'uctive to supply to field winding 12d additional current to prevent the current in machine 6 from substantially exceeding the limiting value.

When the speed setting of divider- 40-- is rapidly *changed to reduce the speed of machine 6 or when it is desired to regeneratively'brake machine 6 to a stop, the high inertia of rolls 9 and the associated equipment causes the voltage of -machine 6 to exceed the voltage of machine :H, causing machine 6 to act as a generator supif plying machine II as a motor, thereby reversing the direction of current flow in armature 6a. This reversal of current renders the voltage of 'interpole winding 60 cumulative with respect to the voltage of resistor 61 and differential with respect to the voltage of resistor 86, so that if this reversed current tends to exceed the maximum value, rectifier 82 permits current to flow through control winding 56c, while rectifier 83 blocks the flow of current through control winding 510. A substantial current thereupon flows through 'reactance winding 56b and resistor 64- to render triode 1| abruptly conductive. action abruptly lowers the potential of terminal 48 and grid 320 to decrease the conductivity of triode 32 and thereby unbalance bridge .23 to This render triodes I4 conductive. -Triodes 14 thereupon supply more current to field winding I to increase the voltage of armature .Ha and thereby prevent the current in machine 6 from substantially exceeding the maximum value.

If resistor 43 was not utilized and grid-53m 6 wascensequentlyconnected directly to anode 4 la, the above described decrease in the potential of terminal '48 and g'rid' 3'2c might notproduce the desired unbalance of bridge 23, since, if triode 5 4| was fully conductive, the potential of grid 31c wouldbe at its lowest value and even if triode H was-fully conductive, the potential of terminal "48" and grid 320 could not decrease below' 'the potential of grid 310-130 unbalance bridge 23 to 0 produce the desired current limiting action.

-'However, with resistor 43 connected as-shown andwith triode H fully conductive as described above, the voltage drop .acrossresistor 43 causes the'potential 0f terminal 48 'to be lower than 15 the potential of terminal 45 independently :of the state of conductivity of triode 4|, so that bridge '23 is unbalanced to produce the desired current limiting action.

Altho'u-gh but one embodiment of the present ,39 invention has been illustrated and described; it

will be apparent to thosesk-illed in the art that various changes andmodifications may be made therein without departing from thespirit of the invention or the scope of the appended claims. 25 Features disclosed but not claimed hereinare claimed in application of Thomas H. Bloodworth, Serial Number 229,329, filed June 1, -1951,'now Patent No. 2,632,139.

It is claimed anddesired-to secure by Letters Patent:

'1. In a system for-maintaining an operating condition of a dynamoelectric machine substantially constant at a predetermined value, the combination of a first sourc for supplying current to said machine, means for reversing the direction of current flow in-said machine, first electric valve means having a'first anode, a first 'cathode and a first controlgrid, second electric valve means having a second anode, a second cathode 4o a seconcl'control grid, a source of "unidirect-io'nal energizing voltage, means connecting the secondsaid source to said first and said second valve means including a connection of negligible impedance between the second said source and saidcathodes, a first resistor connected inseries with said-first anode and said source ofunidirectional voltage, a second resistor and a third insistor serially connected with each other between said-second anode andsaid source of unidirectional voltage, a first terminalbetween said first resistor andsaid first anode, a second terminal between saidsecond and said third resistors, con- -trol meansconnccted to said first and said second terminals to be energized in dependenc upon the 5 polarity and magnitude of the potential difference between said first and said second terminals 'ior controlling the flowof current from said first souice'to said machine, meansconnected-to said m-achine 'andto-said second grid for varying the potential of said second terminal in response to variations in said operating condition fr'om-said predetermined value while maintaining the potential-of said-first terminal at a constant value,

and limiting means connected to said machine 5-and to said first and second valve means-for abruptly decreasing the potential of one of-*said terminals when said machine current reaches --a=.=predetermined maximum value, the potential of said-first terminal being abruptly decreased 'mwhen said current'reaches said maximum value of one polarity and the potential ofsaid second terminal'being abruptly. decreased when-said current reaches said maximum value of the 'other polarity, whereby-when the potential cfsaid first terminal= is decreased by said limiting meang-the 7 voltage drop across said third resistor causes the potential of said first terminal to be lower than the potential of said second terminal independently of the state of conductivity of said second valve means.

2. In a system for maintaining an operating condition of a dynamoelectric machine substantially constant at a predetermined value, the combination of a first source for supplying current to said machine, means for reversing the direction of current flow in said machine, first electric valve means and second electric valve means for controlling the flow of said current to said machine, said first valve means having a first control grid and said second valve means having a second control grid, third electric valve means having a third anode, a third cathode and a third control grid, fourth electric valve means having a fourth anode, a fourth cathode and a fourth control grid, a second source of unidirectional energizing voltage, means connecting said second source to said third and fourth valve means including a connection of negligible im pedance between said second source and said third and fourth cathodes, a first resistor connecting said third anod to said second source, a second resistor and a third resistor serially connected with each other between said fourth anode and said second source, means connecting said first grid to a first terminal between said first resistor and said third anode to vary the conductivity of said first valve means in dependence upon the potential of said first terminal, means connecting said second grid to a second terminal between said second and said third resistors to vary the conductivity of said second valve means in dependence upon the potential of said second terminal, means connected to said machine and to said fourth grid for varying the potential of said second terminal in response to variations in said operating condition from said predetermined value while maintaining the potential of said first terminal at a constant value to vary the current supplied to said machine from said first source, and limiting means connected to said machine and to said third and fourth anodes for abruptly decreasing the potential of one of said terminals when said machine current reaches a predetermined maximum value, the potential of said first terminal being abruptly decreased when said current reaches a predetermined maximum value of one polarity and the potential of said second terminal being abruptly decreased when said current reaches a predetermined maximum value of the other polarity, whereby when the potential of said first terminal is decreased by said limiting means the voltage drop across said third resistor causes the potential of said first terminal to be lower than the potential of said second terminal independently of the state of conductivity of said fourth triode.

3. In a system for maintaining an operating condition of a dynamoelectric machine substantially constant at a predetermined value, the combination of a first source for supplying current to said machine, means for reversing the direction or current flow in said machine, a pair of differentially acting field winding for controlling the flow of said current to said machine, first electric valve means for controlling the energiz-ation of one of said field windings, said first valve means having a first control grid, second electric valve means for controlling the energization of the other of said field windings, said second valve means having a second control grid.

third electric valve means having a third anode, a third cathode and a third control grid, fourth electric valve means having a fourth anode, a fourth cathode and a fourth control grid, a second source of energizing voltage, means connecting said second source to said third and fourth valve means including a connection of negligible impedance between said second source and said third and fourth cathodes, a first resistor connecting said third anode to said second source, a second resistor and a third resistor serially connected with each other between said fourth anode and said second source, means connecting said first grid to a first terminal between said first resistor and said third anode to vary the conductivity of said first valve means in dependence upon the potential of said first terminal, means connecting said second grid to a second terminal between said second and said third resistors to vary the conductivity of said second valve means in dependence upon a potential of said second terminal, means connected to said machine and to said fourth grid for varying the potential of said second terminal in response to variations in said operating condition from said predetermined value While maintaining the potential of said first terminal at a constant value to vary the energization of said field windings to maintain said operating condition substantially constant at said predetermined value, and limiting means connected to said machine and to said third and fourth anodes for abruptly decreasing the potential or one of said terminals when said machine current reaches a predetermined maximum value, the potential of said first terminal being abruptl decreased when said current reaches a predetermined maximum value of one polarity and the potential of said second terminal being abruptly decreased when said current reaches a predetermined maximum value of the other polarity, whereby when the potential of said first terminal is decreased by said limiting means the voltage drop across said third resistor causes the potential of said first terminal to be lower than the potential of said second terminal independently of the state of conductivity of said fourth valve means.

4. In a system for maintaining an operating condition of a dynamoelectric machine substantially constant at a predetermined value, the combination of a first source for supplying current to said machine, means for reversing the direction of current flow in said machine, first electric valve means and second electric valve means for controlling the flow of said current to said machine, said first valve means having a first control grid and said second valve means having a second control grid, third electric valve means having a third anode, a third cathode and a third control grid, fourth electric valve means having a fourth anode, a fourth cathode and a fourth control grid, a second source of voltage, a first resistor connecting said third cathode to said second source, a second resistor connecting said fourth cathode to said second source, a first terminal between said third cathode and said first resistor, a second terminal between said fourth cathode and said second resistor, a third resistor and a fourth resistor serially connected with each other between said first and second terminals, means connecting said first grid to said first terminal, means connecting said second grid to said second terminal, fifth electric valve means having a fifth anode, a fifth cathode and a fifth control grid, sixth electric valve means having a 9 sixth anode, a sixth cathode and a sixth control grid, means connecting said fifth and said sixth valve means to said second source including a connection of negligible impedance between said second source and said fifth and sixth cathodes, a fifth resistor connecting said fifth anode to said second source, a sixth resistor and a seventh resistor serially connected with each other between said sixth anode and said second source, means connecting said third grid to a third terminal between said fifth resistor and said fifth anode to vary the conductivity of said first valve means in dependence upon the potential of said third terminal, means connecting said fourth grid to a fourth terminal between said sixth and said seventh resistors to vary the conductivity of said second valve means in dependence upon the potential of said fourth terminal, means connected to said machine and to said sixth grid for varying the potential of said fourth terminal in response to variation in said operating condition from said predetermined value While maintaining the potential of said third terminal at a constant value to vary the current supplied to said machine, and limiting means connected to said machine and to said fifth and sixth anodes for abruptly decreasing the potential of said third or said fourth terminal when said machine current reaches a predetermined maximum value, the potential of said third terminal being abruptly decreased when said current reaches a predetermined maximum value of one polarity and the potential of said fourth terminal being abruptly decreased when said current reaches a predetermined maximum value of the other polarity, whereby when the potential of said third terminal is decreased by said limiting means the voltage drop across said seventh resistor causes the potential of said third terminal to be lower than the potential of said fourth terminal independently of the state of conductivity of said sixth valve means.

ALLAN C. HALTER.

References Cited in the file of this patent UNITED STATES PATENTS Number 

